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[v3,2/3] depmod: prevent module dependency files corruption due to parallel invocation.

Message ID 20181217224629.22687-3-msuchanek@suse.de (mailing list archive)
State New, archived
Headers show
Series Fix dependency file corruption with parallel depmod invocation | expand

Commit Message

Michal Suchánek Dec. 17, 2018, 10:46 p.m. UTC
Depmod does not use unique filename for temporary files. There is no
guarantee the user does not attempt to run mutiple depmod processes in
parallel. If that happens a temporary file might be created by
depmod(1st), truncated by depmod(2nd), and renamed to final name by
depmod(1st) resulting in corrupted file seen by user.

Due to missing mkstempat() this is more complex than it should be.
Adding PID and timestamp to the filename should be reasonably reliable.
Adding O_EXCL as mkstemp does fails creating the file rather than
corrupting existing file.

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
 - remove superfluous code to terminate the string - snprintf should do
 - remove superfluous O_TRUNC - not needed with O_EXCL
 tools/depmod.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
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diff --git a/tools/depmod.c b/tools/depmod.c
index 18c0d61b2db3..0f7e33ccfd59 100644
--- a/tools/depmod.c
+++ b/tools/depmod.c
@@ -29,6 +29,7 @@ 
 #include <string.h>
 #include <unistd.h>
 #include <sys/stat.h>
+#include <sys/time.h>
 #include <sys/utsname.h>
 #include <shared/array.h>
@@ -2398,6 +2399,9 @@  static int depmod_output(struct depmod *depmod, FILE *out)
 	const char *dname = depmod->cfg->dirname;
 	int dfd, err = 0;
+	struct timeval tv;
+	gettimeofday(&tv, NULL);
 	if (out != NULL)
 		dfd = -1;
@@ -2416,11 +2420,12 @@  static int depmod_output(struct depmod *depmod, FILE *out)
 		int r, ferr;
 		if (fp == NULL) {
-			int flags = O_CREAT | O_TRUNC | O_WRONLY;
+			int flags = O_CREAT | O_EXCL | O_WRONLY;
 			int mode = 0644;
 			int fd;
-			snprintf(tmp, sizeof(tmp), "%s.tmp", itr->name);
+			snprintf(tmp, sizeof(tmp), "%s.%i.%li.%li", itr->name, getpid(),
+					tv.tv_usec, tv.tv_sec);
 			fd = openat(dfd, tmp, flags, mode);
 			if (fd < 0) {
 				ERR("openat(%s, %s, %o, %o): %m\n",